The prior art has disclosed binocular field glasses comprising a first housing part and a second housing part. A first optical subsystem for a first eye of a user is arranged in the first housing part. A second optical subsystem for a second eye of a user is arranged in the second housing part. The first housing part and the second housing part are connected to one another by means of a folding bridge. The folding bridge has a first hinge part arranged on the first housing part. The folding bridge furthermore has a second hinge part arranged on the second housing part. The folding bridge renders it possible to set an intraocular distance such that the first housing part and the second housing part are arranged relative to one another such that the first housing part is arranged in front of one of the two eyes of the user and that the second housing part is arranged in front of the other one of the two eyes of the user.
In the text above, and also in the text below, an optical system is understood to mean not only binocular field glasses but rather any optical system, i.e., for example, also a monocular optical system, particularly in the form of a telescope.
The image captured by an observer through the telescope or the field glasses is often perceived to be shaking because trembling movements or rotational movements of the hands of the user, and also movements underfoot, in turn cause movements of the optical system. In order to avoid this, it is known to stabilize images in an optical system. Known solutions use stabilizing apparatuses for stabilizing the image by means of a mechanical apparatus and/or an electronic apparatus.
DE 23 53 101 C3 has disclosed an optical system in the form of a telescope, which has an objective, an image stabilizing unit in the form of a prism erecting system and an eyepiece. The prism erecting system is mounted in cardan-joint fashion in a housing of the telescope. This is understood to mean that the prism erecting system is arranged in the housing of the telescope such that the prism erecting system is mounted such that it can rotate about two axes arranged at right angles to one another. For the rotatable mounting, use is generally made of a device which is referred to as a cardan-type mount. A hinge point of the prism erecting system, mounted in a cardan-joint fashion in the housing, is arranged centrally between an image-side main plane of the objective and an object-side main plane of the eyepiece. The prism erecting system, mounted in a cardan-joint fashion, is not moved by occurring rotational-trembling movements as a result of its inertia. It therefore remains fixed in space. This is how an image deterioration which occurs as a result of the rotational-trembling movement of the housing is compensated for.
DE 39 33 255 C2 discloses binocular field glasses with an image stabilization having a prism erecting system. The prism erecting system has Porro prisms, which respectively have one tilt axis. The Porro prisms are designed such that they can pivot about their respective tilt axis. Motors are provided for pivoting the Porro prisms. The pivoting is brought about dependent on a trembling movement which causes a shaking of an observed image.
A further optical system with an image stabilizing unit is known from U.S. Pat. No. 5,910,859. The image stabilizing unit of this optical system is designed in the form of an erecting system, which is arranged at an optically neutral point centrally between an objective and an eyepiece. An optically neutral point is understood to mean a point about which the objective and the eyepiece can be rotated in relative fashion in space without the position of an image of an object being displaced, with the erecting system remaining fixed in space. The erecting system is moveably arranged about the optically neutral point and about two axes which are arranged perpendicular to the optical axis. If the erecting system is now kept stably in space, even in the case of a trembling movement, then the image of an object is also stabilized by means of this known optical system when the object is observed. The optically neutral point can also be described as follows: an optically neutral point is understood to mean a point on an optical axis between an objective and an eyepiece about which an image stabilizing unit is rotatably arranged such that in the case of a rotational-trembling movement about any point the direction of the image of an object observed through the objective and the eyepiece remains fixed in space, just like the image stabilizing unit.
The prior art has also disclosed field glasses which have a rigid housing, in which a first optical subsystem and a second optical subsystem are arranged for both eyes of a user. In order to stabilize an image on account of the problem already mentioned above, a single image stabilizing unit is arranged in the housing, said stabilizing unit being used for image stabilization both in respect of the first optical subsystem and in respect of the second optical subsystem. As a result of the design, this single image stabilizing unit is at least as wide as the distance of the first optical subsystem from the second optical subsystem. In the known field glasses provision is made for the possibility of setting the interocular distance of a user. To this end, rotatable rhombic prisms are arranged in the rigid housing, the former being installed between the rigid housing and an eyepiece. If the rhombic prisms are rotated, there is a change in the spacing of the eyepieces so that the interocular distance of a user can be set.
Now, rotational-angle detectors are used in the above-described known field glasses in order to establish a trembling movement or a further movement of the field glasses. By means of these rotational-angle detectors it is possible to measure rotational-trembling movements about two axes which are aligned perpendicular to the optical axis of the field glasses. The two axes (namely a first measurement axis and a second measurement axis) are likewise aligned perpendicular to one another. For image stabilization purposes, the known field glasses are now provided with a control device, which is arranged in the rigid housing and adjusts the image stabilizing unit for image stabilization purposes. In the process, the image stabilizing unit is moved along the optical axis. Furthermore, provision is made for the image stabilizing unit to be rotated about a first axis of rotation and about a second axis of rotation, wherein the first axis of rotation and the second axis of rotation are aligned perpendicular to the optical axis. However, in order to determine the rotational angle precisely about which the image stabilizing unit is to be rotated about the first axis of rotation and the second axis of rotation, it is necessary to take into account the relative position of the first measurement axis and the second measurement axis of a rotational-angle detector with respect to the first axis of rotation and the second axis of rotation of the image stabilizing unit. In the field glasses with a rigid housing known from the prior art, it is possible to design the relative position of the first axis of rotation and the second axis of rotation as well as of the first measurement axis and the second measurement axis such that the two pairs of axes coincide. The rotational angle can then be determined easily.
Accordingly, it would be desirable to specify a method for setting a position of an image stabilizing unit which is arranged in an optical system that has a folding bridge. Moreover, it would be desirable to specify an optical system which is suitable for carrying out this method.